This disclosure relates to improvements in positioning systems for controlling mobile load-handling clamps of the type normally mounted on lift trucks or other industrial vehicles for clamping rectilinear loads such as cartons, or cylindrical loads such as paper rolls. In order to ensure damage-free clamping and subsequent handling of such loads, it is critical that the pre-engagement positions of the opposed clamping surfaces of such clamps be substantially correct for the particular load to be clamped. For example, if the pre-engagement positions of the opposed clamping surfaces in the clamp's direction of forward approach toward the load are not at least approximately correct relative to the particular load being clamped, unacceptable pressure concentrations and pressure insufficiencies can occur at different areas of the clamping surfaces when the load is engaged, causing various problems ranging from excessive compression of the load to slippage of the load during subsequent lifting, transporting and depositing of the load. Alternatively, if the pre-engagement positions of the clamping surfaces are not at least approximately vertically correct relative to a carton, the clamping surfaces may fail to engage the carton's internal reinforcement structure resulting in excessive compression of unreinforced portions of the carton. Or, if the pre-engagement positions of paper roll clamping surfaces are not sufficiently centered vertically relative to the paper roll's center of gravity, the paper roll and its transporting vehicle can become unstable when the roll is rotated from a vertical to a horizontal position. In addition, if the pre-engagement spacing between opposed clamping surfaces during their forward approach to the load is too narrow, it can cause gouging or abrading of the load or, if the spacing is too wide, it can cause similar damage to adjacent loads. Furthermore, unsymmetrical side-to-side pre-engagement positioning of the clamping surfaces can cause the load, or the clamp and vehicle, to slide sideways and cause damage during clamping engagement of the load.
Prior load-clamping systems have relied heavily on the operator's judgment and visibility of the clamping surfaces to produce correct pre-engagement positions of vehicle-mounted clamping surfaces relative to different loads of variable sizes and shapes. This is an extremely difficult task for an operator from his visually restricted location on a lift truck operator's seat.
Different types of visual or audible sensor-generated guidance aids have sometimes been provided to help the operator in this task, but such aids are generally reliant only on sensing external surfaces of the load, rather than determining internal features of the load which may be determinative of correct clamping surface positioning. The same has generally been true with respect to automatically-guided vehicle-mounted load clamps. Such approaches based exclusively on external load surfaces are often insufficient to ensure that the clamping surfaces will engage different loads in respective different correct positions to overcome the foregoing problems.